SMALL DAMS

FRENCH COMMITTEE ON LARGE DAMS
COMITÉ FRANÇAIS DES GRANDS BARRAGES
SMALL DAMS
Guidelines for Design,
Construction and Monitoring
Coordination : Gérard Degoutte

FRENCH COMMITTEE ON LARGE DAMS
COMITÉ FRANÇAIS DES GRANDS BARRAGES
SMALL DAMS
Guidelines for Design, Construction
and Monitoring
Coordination : Gérard DEGOUTTE (ENGREF)
Réalisé avec la participation financière du ministère
de l'Agriculture et de la Pêche
Direction de l'Espace Rural et de la Forêt
- France -

PHOTOGRAPH REFERENCES
Cover: CACG, l'Arrêt-Darré dam (Hautes-Pyrénées, France)
Ph. 19 : C.A.C.G.
Ph. 15 – 18 : CARA
Ph. 1, 2, 4, 7, 9 – 10 : E. Alonso
Ph. 3, 6, 11, 20, 21 – 22 : G. Degoutte
Ph. 5, 8, 12, 13, 14 – 23 : P. Royet
Small dams, guidelines for design, construction and monitoring :
© Copyright 2002 Cemagref Editions and Engref (France), with French Committee on Large Dams - All rights
reserved - Coordination : Gérard Degoutte. Translation : Links, Le Bourget du Lac (France) and Robert Chadwick
(UK). First published 2002, on digital disc only. ISBN 2-85362-551-6 - Cover : Barrage de l'Arrêt-Darre,
Compagnie d'aménagement des coteaux de Gascogne. Dépôt légal : 1 er trimestre 2002
Translated from french original book "Petits barrages, recommandations pour la conception, la réalisation
et le suivi". © Copyright 1997 Cemagref Éditions and ENGREF (France), with French Committee
on Large Dams - ISBN 2-85362-448-X - All rights reserved - Coordination : Gérard Degoutte.

M EMBERS OF THE WORKING GROUP
C HAIRMAN, WORKING GROUP: G. DEGOUTTE (ENGREF)
Group Geological and geotechnical studies
Chairman:
P. BRUNEL (CARA)
Committee Members:
Group Fill dams
Chairman:
Committee Members:
G. MICHEL (SCP),
E. ALONSO (Cemagref), J.-P. BECUE (SAFEGE), J.-L. BRODIN (CACG),
B. COUTURIER (BRL), D. LAUTRIN (Cemagref), G. MICHEL (SCP)
E. ALONSO (Cemagref)
J.-P. BECUE (SAFEGE), G. BOLLE (expert), J.-L. BRODIN (CACG),
P. BRUNEL (CARA), A. CASSARD (DDAF Bas-Rhin),
G. DEGOUTTE (ENGREF), M. DORÉ (MECASOL),
D. LAUTRIN (Cemagref), J. LEFEBVRE (ingénieur conseil),
P. ROYET (Cemagref), G. TRATAPEL (CNR)
Group Small concrete dams
Chairman:
P. ROYET (Cemagref)
Committee Members:
G. DEGOUTTE (ENGREF), M. GIRARD (SOMIVAL), M. LINO (ISL),
J. TEYSSIEUX (COYNE & BELLIER), G. TRATAPEL (CNR)
Group Life of the dams
Chairman:
Ph. VINCENT (EDF)
Committee Members:
A. EMERIAU (DDAF Lot-et-Garonne), Ph. MARTIN (CACG),
G. MICHEL (SCP), P. ROYET (Cemagref)
Chapter Choice of site and type of dams
J.-P. BECUE (SAFEGE), G. DEGOUTTE (ENGREF) and D. LAUTRIN (Cemagref)
Chapter Preliminary determination of design flood
J. LAVABRE (Cemagref)
Chapter Management of water quality
H. BEUFFE, A. DUTARTRE, Y. SOUCHON, S. VALENTIN (Cemagref),
A. GRÉGOIRE (EDF), A. HÉTIER (CACG) and M. LAFFORGUE (AquaTechnique)

M EMBERS OF THE READING PANEL
† A. GOUBET, president of CFBG
D. BISTER (EDF)
A. CARRERE (COB)
P. DUPEUBLE (BACHY)
J.J. FRY (EDF)
P. HABIB (former president of International Society on Rocks Mechanics)
F. LACROIX (Cemagref)
P. LE DELLIOU (BETCGB)
† P. LONDE (emeritus president of International Commision
Large Dams)
P. MALIVERNEY (EDF)

P REFACE
These guidelines for the design and construction of small dams have been
drafted under the aegis of the French Committee on Large Dams. Small
dams are conventionally defined as dams less than approximately 25 metres
high.
The designer of a small dam may face a difficult task because he will not
have access to the design and monitoring resources commonly deployed
for larger dams.
The recommendations and advice in these guidelines have been drawn
up on the basis of the climate, population and economic conditions found
in France. They may require some modification if used in a different context.
For example, safety criteria may be relaxed if the valley downstream of
the dam is sparsely populated; greater caution may be required in the
absence of abundant rainfall and streamflow records; and some of the
arrangements recommended may be considered needlessly costly luxuries.
Nevertheless, the guidelines provide a consistent foundation on which
country-specific alternatives can be built up. It is thus of undeniable general
interest, and the French Committee has decided to support an English
language version.
† André GOUBET

TABLE OF CONTENTS
Foreword - What need for guidelines
for small dams? ..................................................................................... 13
WHAT DAMS?........................................................................................ 13
FEATURES SPECIFIC TO SMALL DAMS .............................................................. 14
WHAT IS MEANT BY "SMALL DAM"? ............................................................. 14
DAM SIZE AND SAFETY ............................................................................. 15
ASPECTS DISCUSSED ................................................................................ 16
Chap. I - Choice of site and type of dam .............................................. 17
TOPOGRAPHY AND INFLOW IN THE CATCHMENT AREA ...................................... 18
MORPHOLOGY OF THE RIVER VALLEY............................................................. 18
GEOLOGY AND FOUNDATION CONDITIONS .................................................... 18
Rock foundations .................................................................................... 19
Gravel foundations .................................................................................. 19
Sandy-silt foundations ............................................................................. 19
Clay foundations ..................................................................................... 19
AVAILABLE MATERIALS .............................................................................. 20
FLOODS AND FLOOD DISCHARGE STRUCTURES ................................................ 21
ECONOMIC CRITERIA ................................................................................ 21
CONCLUSIONS ON SELECTING A TYPE OF DAM ................................................ 22
Chap. II - Preliminary determination of design flood ........................... 23
PRELIMINARIES........................................................................................ 24
DESIGN FLOOD AND SAFETY FLOOD ............................................................. 25
THE GRADEX METHOD ............................................................................. 26
Assumptions of the Gradex method ......................................................... 26
Difficulties in applying the Gradex method............................................. 27
THE AGREGEE MODEL ............................................................................... 28
THE PMP - PMF METHOD ...................................................................... 29
THE SHYPRE MODEL: SIMULATION OF FLOOD SCENARIOS ................................... 29
EMPIRICAL FORMULAS AND REGIONAL FORMULAS ............................................ 30
The Francou-Rodier envelope curve1 ...................................................... 30
Synthesis of flow with a recurrence interval of 1000 years calculated
with the Gradex method.......................................................................... 31

T able of contents
RAINFALL RUNOFF ANALYSIS IN A WELL DOCUMENTED CATCHMENT ...................... 31
Presentation of the catchment area ......................................................... 32
Application of the Gradex method .......................................................... 32
Catchment retention ............................................................................... 32
Statistical rainfall and runoff distributions................................................ 33
Peak/mean flow coefficients ................................................................... 34
Conclusion .............................................................................................. 34
Design flood hydrograph ......................................................................... 34
BIBLIOGRAPHY ....................................................................................... 36
8
Chap. III - Geological and geotechnical studies .................................. 37
PRELIMINARIES........................................................................................ 37
TECHNIQUES.......................................................................................... 38
Site inventory.......................................................................................... 38
Surveying ................................................................................................ 39
Photogeology .......................................................................................... 40
Geological mapping ............................................................................... 40
Trial pits .................................................................................................. 40
Geophysical studies ................................................................................ 41
Core sampling ......................................................................................... 42
Geotechnical laboratory tests .................................................................. 46
Site tests and measurements .................................................................... 47
RECOMMENDATIONS FOR CONDUCT OF THE STUDIES ........................................ 48
Site identification and selection .............................................................. 48
Geological surface study ......................................................................... 49
Geological feasibility study .................................................................... 52
Geological and geotechnical studies in the preliminary design stage ...... 57
Geological and geotechnical studies in the tender design stage .............. 60
Geology and geotechnics in the construction phase ................................ 61
Geological supervision during construction ............................................. 62
BIBLIOGRAPHY ....................................................................................... 66
Chap. IV - Fill dams ............................................................................... 67
TYPES OF FILL DAMS ................................................................................. 67
GEOTECHNICAL STUDIES ........................................................................... 68
CHOICE OF AN EARTHFILL DAM ................................................................... 70
DAM FOUNDATION TREATMENT .................................................................. 71
Foundation watertightness ....................................................................... 71
Foundation drainage ................................................................................ 72

Table of contents
FILL DAM DESIGN .................................................................................... 73
Croos-section, crest width, freeboard ....................................................... 73
Protection of faces and crest ................................................................... 75
Filters and drains ..................................................................................... 77
Man-made watertightening systems ........................................................ 81
STABILITY ANALYSIS ................................................................................. 82
Actions ................................................................................................... 82
Stability calculations .............................................................................. 83
ACCOUNTING FOR SEISMIC ACTIVITY ............................................................ 87
Design earthquake and methods for dam stability calculation ................. 87
Pseudo-static method .............................................................................. 88
Methods using the dynamic behaviour of soils ........................................ 89
Special construction techniques for the foundation and the fill ................ 89
MONITORING SYSTEM .............................................................................. 90
Monitoring devices for small dams .......................................................... 90
Choice of a monitoring system ................................................................ 92
WATER INTAKE AND OUTLET ...................................................................... 93
Recommendations common to systems consisting of a pipe .................... 93
Case-by-case recommendations (minimum system) ................................. 94
SPILLWAY .............................................................................................. 95
Design of the free overflow sill ............................................................... 96
Location and dimension .......................................................................... 97
Solutions tailored to very small dams ...................................................... 99
Behaviour of ancillary structures in earthquakes ...................................... 99
TENDERING AND DAM CONSTRUCTION ....................................................... 100
Tendering .............................................................................................. 100
Construction principles to be stipulated in the particular
technical clauses .................................................................................. 101
Test section ........................................................................................... 102
Works supervision ................................................................................. 104
SPECIFIC FEATURES OF VERY LONG DYKES ..................................................... 107
Special features in the site investigation phase ..................................... 108
Specific features in the design phase .................................................... 108
ELEMENTS ON COST ............................................................................... 109
Capital costs ......................................................................................... 109
Cost of maintenance and surveillance ................................................... 110
BIBLIOGRAPHY ..................................................................................... 111
9

T able of contents
10
Chap. V - Small concrete dams ........................................................... 113
CHOICE OF A CONCRETE DAM .................................................................. 114
Why opt for a rigid dam structure?......................................................... 114
Mechanical functioning of rigid dams ................................................... 114
Materials used: history .......................................................................... 116
Conclusions on the choice of a concrete dam ....................................... 119
THE CLASSIC GRAVITY DAM (CVC OR RCC) ............................................... 120
Foundation ............................................................................................ 120
Foundation treatment ............................................................................ 121
Drainage ............................................................................................... 122
Stability analysis ................................................................................... 122
Construction techniques for conventional concrete dams ...................... 127
Monitoring systems ............................................................................... 129
SOME EXAMPLES OF RECENTLY BUILT RCC DAMS ............................................. 129
Riou dam .............................................................................................. 130
Villaumur dam ...................................................................................... 131
El Koreima dam .................................................................................... 132
Louberria dam ....................................................................................... 133
Mykonos I dam ..................................................................................... 133
BARRAGE TYPE DAMS ............................................................................. 134
Foreword ............................................................................................... 134
Dimensioning principles........................................................................ 135
Construction techniques ........................................................................ 136
Inflatable barrages ................................................................................ 136
TENDERING AND TRIAL EMBANKMENTS ........................................................ 138
BIBLIOGRAPHY ..................................................................................... 139
Chap. VI - Management of water quality ........................................... 141
MANAGEMENT OF WATER QUALITY RESERVOIRS ............................................. 141
Eutrophication in man made reservoirs .................................................. 142
Aquatic fauna ....................................................................................... 143
Management and restoration ................................................................. 144
Conclusions on reservoir water quality .................................................. 149
CONSEQUENCES OF COMPENSATION WATER ON FISH LIFE ................................. 150
Effects of reduced flows ........................................................................ 150
Measuring modifications in the physical habitat ................................... 151
Taking ecological effects into account in studies of compensation flow 154
Conclusion: moving towards integrated management............................ 157
BIBLIOGRAPHY ..................................................................................... 157

Table of contents
Chap. VII - Life of the dam.................................................................. 159
SPECIAL FEATURES OF "SMALL DAMS" .......................................................... 160
ROLES OF THE VARIOUS PARTICIPANTS ......................................................... 160
The owner (or the concession holder) .................................................... 160
The operator .......................................................................................... 160
The engineer ......................................................................................... 161
The inspection administration ................................................................ 161
GENERAL SURVEILLANCE PRINCIPLES ........................................................... 162
METHODOLOGY FOR DAM SURVEILLANCE .................................................... 163
Documents on construction ................................................................... 163
Surveillance plan .................................................................................. 163
ORGANISATION OF SURVEILLANCE BY THE OWNER .......................................... 164
Visual inspection .................................................................................. 164
Technical inspections ............................................................................ 165
Monitoring ............................................................................................ 166
Monitoring reports ................................................................................. 166
INSPECTIONS BY THE ADMINISTRATION ........................................................ 167
Annual inspection ................................................................................. 167
Ten year inspections .............................................................................. 167
MAINTENANCE..................................................................................... 168
CONCLUSION ...................................................................................... 168
Dam history .......................................................................................... 168
Surveillance .......................................................................................... 169
Training - Awareness ............................................................................. 169
For new dams ........................................................................................ 169
BIBLIOGRAPHY ..................................................................................... 170
11
Chap. VIII - Conclusion ....................................................................... 171
Geological and geotechnical studies .................................................... 171
Flood data ............................................................................................. 172
Design of earthfill dams ........................................................................ 172
Design of concrete dams ....................................................................... 172
Spillway design ..................................................................................... 172
Surveillance .......................................................................................... 173